1. Field of the Invention
The present invention relates to an aortic graft and method of treating abdominal aneurysms, and particularly relates to a graft and method for intraluminal repairing of aortic aneurysms by positioning the graft inside the aneurysm without the drawbacks of conventional monoiliac or bifurcated aorto iliac grafts, such drawbacks relating to the rotation and misplacement of the graft during the insertion, positioning and installation of the graft inside the aorta.
2. Description of the Prior Art
The aorta is the main trunk of the arterial system, arising from the heart and extending down through the thorax and through the abdomen to divide into two iliac arteries. An abdominal aortic aneurysm is an abnormal dilation of the aortic wall as the aorta passes through the abdomen. The aneurysm must be treated to prevent the rupturing thereof. If left untreated, the aneurysm will eventually cause rupture of the sac with fatal hemorrhaging consequences in a very short time. This leads to the death of the individual suffering the aneurysm and, today, the mortality resulting form this abnormality is so very high that it is causing the physicians to seek for improved new techniques to overcome this problem. While surgery has been the most classical way to approach this problem, the surgical repair of the aortic wall is associated, however, to a high risk, particularly for old patients.
The search for alternative techniques not involving surgery has been a concern of the professionals in the art. U.S. Pat. No. 4,562,596, to Elliot Kornberg et al. discloses an aortic bifurcated graft that is specifically designed for intraluminal insertion and comprising a one-piece generally cylindrical hollow sleeve, that has an upper end to be attached to an upper proximal neck of the aorta, upstream the aneurysm, and a minor and major axis defining two lower legs to be inserted each into a respective iliac artery, downstream of the aneurysm, thus forming a continuous fluid path within the aorta, excluding the affected aortic wall, namely the aneurysm, from the blood flow.
U.S. Pat. No. 4,922,905 relates to a catheter and discloses a tubular endoprosthesis device having a wall structure comprised of a tube-like, knitted open fabric of loosely interlocked loops of metallic filament material, said tube-like fabric being radially inwardly deformed relative to its as-knit form and is capable of progressive permanent deformation with attendant radial expansion by means of the catheter to attach the endoprosthesis inside a blood vessel to be repaired.
WO 83/03752 to Wallsten, Hans Ivar, discloses a prosthesis comprising a one-piece expandable tubular body to be inserted into a vascular vessel.
WO 90/15582 to Trout, Hugh, discloses an aortic graft comprising a substantially cylindrical graft material with attachment means which comprise a plurality of post and hook assemblies to provide firm attachment of the aortic graft against the aortic wall.
Although many graft structures have been developed, all of them have been improved in connection to new materials, new attachment means, stents and/or new devices for placing and installing the graft inside the vessel. However, the location and correct placing of the graft inside a blood vessel, particularly a graft designed for repairing aortic aneurysms, are not an easy task as long as the aorta is the largest vessel with a shape that requires that special consideration is made not only of the dilated wall but also of such portions of the wall in good conditions available for firmly attaching the graft in the aorta.
One obstacle that is found during election of the graft for a given patient is that the length of the aorta is not the same for all patients and, even for the same patient the aorta has an inner diameter at the upper or proximal aortic neck and the iliac arteries have a smaller different diameter. Furthermore, the ratio between the aortic diameter and the iliac diameters are not always the same, therefore it is today necessary to have large number of grafts combining a large number of upper diameters, for the aortic neck, and lower diameters, for the iliac arteries.
The problem of the different sizes and shapes of the aortas is also an important issue at the time of placing the upper end of the graft in the correct site at the aortic proximal neck for obtaining a firm attachment of the graft on the neck and for sealing the graft against the neck of the aorta to avoid any blood flowing by the graft to leak out of the graft into the excluded aneurysm. That is, the blood flow must only circulate restricted to the interior of the graft without any leaking being produced at the attachment site. The graft includes, at each end thereof, an anchoring means, called stents, each stent being firmly attached to each graft end with a portion of each stent protruding beyond the associated end, such protruding portion being designed to be anchored against the aortic or iliac walls. Therefore, if the graft is not long enough, it may be that the stent remains firmly attached to the aortic proximal neck without the end of the graft material being correctly placed and sealed against the aortic neck wall. In this situation, the graft will be firmly retained against the aorta wall but the graft material will not be sealed against the aortic neck at the attachment site. Is not a question, however, of replacing the short graft by a longer graft to solve this problem because an extremely long graft, although covering the entire extension between the upper neck of the aorta and the corresponding iliac arteries, may have an exceeding length that becomes folded within the aorta, forming restricted zones and obstructions to the normal flow of the blood inside the graft.
Another question is that the diameter of the aortic neck must be carefully taken into account at the time of selecting the graft. If the graft is of a diameter insufficient to match the aortic neck diameter, there will be a blood leak trough a gap formed between the graft and the aortic wall. If the graft diameter is in excess, the upper edge of the graft will be folded, forming little gaps against the aortic wall, with the same leakage problems above explained. This problem is somewhat overcome by grafts made of resilient fabric, with stents made of resilient self-expanding material capable of self-expanding to a maximum diameter, or rigid stents made of a material construction that may be deformed by an expandable balloon and keep a final deformed diameter. However, the use of resilient stents are not recommended because the exceeding diameter thereof causes the aortic wall to be permanently subject to an expanding force affecting the aortic wall integrity. The use of rigid stents, although recommendable for the patient's safety, involves some installation problems as below explained.
Another problem to be taken into account when inserting and implanting a graft inside an aorta is that the graft is loaded in a multiple folded condition inside a tubular inserting or positioning device, also called introducer or sheath, a catheter for example, to carry the graft to the site of installation and to deploy the graft by radially expanding the same by any known technique, by an expandable balloon for example. To be firmly retained in the aortic proximal neck and in the corresponding iliac artery, the graft is provided at respective upper and lower ends thereof with anchoring means, as explained above, generally comprised of metal stents capable of firmly attaching the graft against the corresponding vessel wall when the stent is in the expanded condition. During the expansion, however, the upper end of the graft undergoes a rotary movement relative to the lower end of the graft. In addition, the same effect may occur in connection to the lower ends relative to the upper end of the graft. This causes the graft to be implanted with its body twisted and the flow passage defined by the graft being unduly restricted, forming a blockage to the blood flow. The rotation of the graft ends may be produced by the inflation of the balloon which is made of an inelastic material that is multiply folded in the positioning device and, upon inflation, it rotates during deployment. This rotation is transferred to the graft. The rotation induced on the graft may be also produced by the movements of the introducer into the vessel during the deployment and installation of the graft. This twisting effect appears in all grafts, either monoiliac grafts made of a cylindrical material or bi-iliac grafts, that is the bifurcated grafts.
Generally, the conventional grafts, either monoiliac and bi-iliac ones, are made of a fabric material, either of elastic knitted material or inelastic woven material. Although the elastic grafts may accommodate better the several ratios between the different diameters of the aortic neck and the iliac arteries, these grafts are dramatically affected by the problem related to the length of the graft and the twisting effect above disclosed. The grafts made of inelastic woven material are affected by all of the above mentioned drawbacks of the conventional aortic grafts.
In order to at least diminishing the above drawbacks, some bifurcated aorto-iliac grafts having a leg or limb generally longer than the other, have been developed. Thus, the shorter limb is folded within the longest limb inside the catheter and the graft is carried into the aorta. At the appropriate point when the blood flow begins to enter the graft, the shorter leg floats free in the blood stream and it is supposed to be easily directed to the proper position. However, once the upper end of this bifurcated graft is attached to the upper neck of the aorta and the lower end of the longest limb is attached inside the iliac artery through which the aorta has been acceded, the graft frequently results twisted along the upper trunk portion of the one-piece graft and the longest limb. To make the situation worst, the rotation of the trunk portion may have left the free short limb in a position diametrically opposite to the iliac artery that is free to receive said shorter limb. In this position, the longest limb, already attached inside the corresponding artery is interfering the path between the shorter limb and the free artery, thus blocking the path and preventing the shorter limb from being directed to and inserted into the corresponding free iliac artery. Therefore, although the shorter limb may have been not affected by the twisting effect, it is directed to a position that makes impossible to introduce the same into the artery.
While other monoiliac grafts and bifurcated grafts both made of several parts have been also developed, the same have been devised to form resilient-wire structures forming a helical like-spring configuration with an outer synthetic lining. These grafts, however, have a very rigid behavior which causes the same to be practically impossible to be passed through some tortuous blood vessels to reach the aorta and even practically impossible to be properly fixed in the aorta. U.S. Pat. No. 5,609,627 to Goicoechea et al. discloses a bifurcated prosthesis comprised by a wire skeleton constructed in several parts, made of nitinol wire and lined by a fabric graft layer. The nitinol wire, although flexible in a cold state, behaves like a steel wire under the temperature inside a patient's body. As it is also disclosed in this patent, Goicochea also proposes a method to install this graft consisting in placing a first bifurcated part and then enter this part by lower ends of same to introduce additional leg grafts and connect the same to lower openings in the bifurcated part. The risk of puncturing the aorta wall with the guide wire and introducer during this operation is enormous and the task of connecting the several parts inside the aorta is extremely difficult because the bifurcated part is semi-rigid and may adopt any aleatory position that causes the openings of same difficult to be reached.
U.S. Pat. No. 5,628,788 to Pinchuk et al; U.S. Pat. No. 5,632,772 to Alcime et al. and U.S. Pat. No. 5,639,278 to Dereume et al. disclose endoluminal grafts which are both expandable and supportive and are comprised of a supportive stent made of resilient wire elements and cover or liner made of a porous material over or inside the supportive wire structure. The same above explained problems are found in these grafts when trying to fold the same in an introducer, when passing the introducer through tortuous or restricted blood vessels and when fixing the stent to the available aorta wall.
Briefly, when a support-liner composite graft is tried to be accommodated inside a tortuous aorta and, because of this rigidity, the graft does not seat and seal appropriately against the aortic neck as long as the body of the graft is forced through the tortuous aortic lumen and the graft tends to adopt a straight configuration without copying the tortuous or curved aortic lumen. It is very common that this kind of grafts remain fixed in the aortic neck in an inclined configuration because when all the guide wires and introducers are removed from the aorta once the graft has been installed therein, the aorta comes back to its original tortuous configuration. Since the graft can not be accommodated to this configuration, the forces exerted by the aorta to recover its initial position is transferred directly to the graft causing the same to alter its initial connection in the aortic neck. The same alterations occur in the graft legs connected to the main graft portion and the iliac arteries. In addition to the foregoing, it also well known that the aortic neck is not always horizontal and it can be inclined as to the vertical axis of a patient's body. Under these circumstances a wire-made graft like the ones disclosed above can not be accommodated to this inclination. A similar problem is faced when the inner wall of the aortic neck is not entirely circular but has calciferous formations that make the neck inner wall irregular. this irregular perimeter can not be "copied" by a wire made graft, thus leaving portions of the aortic wall without being sealed therefore resulting in leaking of the blood flow. If, to overcome any of these problems relate to irregularities of the aortic neck, the graft is placed in a higher position, upwardly beyond the renal arteries, the flow through these arteries is blocked by the graft supportive construction formed by a dense wire mesh.
Another question related to the use of grafts made from compliant or elastic material is that the connection between the parts conforming the graft is somewhat difficult to be achieved in a safety manner as long as the compliance and elasticity of the connecting materials cause the connection to be easily released if not firmly performed. Thus, this connection requires that barbs, hooks, clips, etc. be used to firmly fix the involved parts without the risk of detaching under the effect of the blood flow and other involved forces. This problem is not found in grafts made of no-compliant or inelastic fabrics because any conventional expandable stent used to make the connection will be expanded against the maximum diameter of the connecting parts exerting an important retaining radial force.
It would be therefore convenient to have an aortic bifurcated graft capable of adapting to all of the size and shape characteristics of most of the aortas. It would also be necessary to find a new aortic graft capable of being installed without undergoing the above mentioned twisting effect and misplacing.